We previously found that high molecular weight polymers 1 could be prepared from 4-(4-hydroxyphenyl)phthalazin-1(2H)-one 2 by reaction with activated halides under conditions generally used for the preparation of poly(aryl ether)s [1, 2] (Scheme 1). The C—N coupling reaction was unexpected since the NH group behaves like a phenolic OH group in this reaction. These polymers are excellent high temperature thermoplastics and are currently being commercialized in China.

We subsequently prepared bisphthalazinone structures such as 3.[3] The polymers obtained by C—N coupling were very difficult to process, because of insolubility due to crystallinity and very high glass transition temperatures.

This problem was recently alleviated by the synthesis of the more flexible monomers 4 to yield a series of polymers 5.[4]

A series of polymers have also been synthesized from the closely related pyridazinones.[5] and polyfluorinated phthalazinones.[6]
We have recently found that, at elevated temperatures, biscarbazoles also react with activated halides to give high molecular weight polymers that are thermally stable (Scheme 3). The polymers are highly fluorescent with emission in the blue region of the spectrum.[7] The polymer shown in Scheme 3 is a rigid structure with little flexibility. We have recently reported more flexible biscarbazoles that yield soluble polymers after a C—N coupling polymerization reaction.[8]

We have also found that the NH group in benzimidazoles will \ undergo a C—N coupling reaction with activated halides, e.g. bis(4-fluorophenyl sulfone.[9, 10] High molecular weight, linear polymers (e.g. 9) were formed from bisbenzimidazoles (e.g. 1,3-bis(1H-benzo[d]imidazol-2-yl)benzene 8 as shown) (Scheme 4).

The homopolymers and copolymers have very high Tgs and they are very thermally stable. The Tg of the copolymers ranges between 210° C. (poly(arylene ether) and 296° C. depending on the concentration of the biphenol.
Polybenzimidazolones
The reaction of 1H-benzo[d]imidazol-2(3H)-one 10 with aliphatic chlorides and acyl halides has been described.[11] Benzoimidazolone has been reported to be stable toward acid or base hydrolysis under normal conditions.[12] The reaction with 1,4-bis(chloromethyl)benzene in DMF in the presence of potassium carbonate, for example, is reported to give a polymer with a melt temperature of 213° C. A polymer from 1,5-dichloropentane was also prepared but no properties were given. Reactions with acid chlorides were also carried out. In most cases quite low yields of polymers and no information on molecular weights was provided. The alkylation of benzimidazolone has also been described in a number of other papers.[13-15] The reaction of benzimidazolones with unactivated aromatic halides (e.g. 4-bromoanisole) with a CuI catalyst in toluene at reflux for 24 hours gave an 82% yield of the diaryl-substituted product. Since almost quantitative yields are required in order to synthesize high molecular weight linear polymers, the yields are well short of the yields that would be required to give a high molecular weight polymer using appropriately disubstituted bromo-compounds.[16]